If you’re wondering how to get to the Halls Of Pain in Diablo 2: Resurrected, then this is probably because you’ve reached the Glacial Trail waypoint already, but didn’t find the Halls of Pain waypoint along the way. The Halls of Pain is an area you’ll pass through during the Betrayal of Harrogath quest, which is optional, and that’s probably why you missed it.
To get to the Halls of Pain, start the Betrayal of Harrogath quest by talking to Anya after completing the Prison of Ice quest, then go through the portal she creates to get to Nihlathak’s Temple. Proceed through the temple grounds and in through the entrance. Inside you’ll find stairs down to the Halls Of Anguish. The Halls of Anguish is randomly generated, but somewhere in here you’ll find the stairs down to the Halls of Pain.
It’s worth noting that a lot of players deliberately skip the Betrayal of Harrogath quest, particularly on Nightmare, Hell, and Hardcore, because Nihlathak is a really deadly adversary, so it may not be worth the risk. Even among players that do attempt the quest, many deliberately avoid activating the Hall of Pain waypoint because doing so de-activates Anya’s portal. Anya’s portal is useful in resetting her selection of Claws and in farming Piddleskin in Nihlathak’s Temple. However, if you want the Explorer Reporting trophy/achievement, then you’ll need to activate it.